Circuit breakers dashpot mechanism



1957 J. A. OPPEL 2,804,513

CIRCUIT BREAKERS DASHPOT MECHANISM Filed Dec. 51, 1953 23 F' .l. n i...

L? a 4 r 22 LJ I u 1 REVERS/ E FLU/D A DAYS/ P07 MECH/M/ISM 9 ZONE TIME

canlrncrs CONTACTS FULLY OPEN Inventor:

by I

Q/ His A torney.

CIRCUIT BREAKERS nAsrrror MrcrrANrsM John A. Oppel, Aidan, Pa., assignorto General Electric Company, a corporation of New York ApplicationDecember 31, 1953, Serial No. 401,539

16 Claims. (Cl. Mid-34) This invention relates to a dashpot mechanismand, more particularly, to a double-acting dashpot mechanism forgoverning the forward and reverse travel between rest positions of amovable member, such as, the movable contact of a circuit breaker.

In order to illustrate my invention, I will describe apparatusparticularly adapted for carrying it into effect in an electric circuitbreaker of a particular type. It is to be understood, however, thatcertain features of the invention are not limited to this particularapplication but are of general application wherever it is desired tocontrol the movement of a relatively movable body between spaced apartpositions of rest.

In the usual fluid blast type of circuit breaker, the circuit breakercontacts are initially separated to draw an arc, and as the contactseparation continues, the arc is subjected to an arc-extinguishing fluidblast action, after which further separation of the contacts providessufficient isolation between the contacts to prevent restriking of thearc. To produce optimum interrupting characteristics in such a circuitbreaker, it is desirable that the movable contact be subjected to rapidinitial acceleration for separating the contacts and establishing thearc. As this separation continues and the movable contact enters thearcing zone, the moving contact should be retarded so that the arc maybe subjected to effective blasting action whereby to extinguish the are.As this extinction occurs, rapid opening speed should be resumed andcontinued until the movable contact is smoothly decelerated at the endof its opening stroke.

In contrast to this opening operation, contact closing operation shouldbe effected at a high speed without retardation in the arcing zone.Thus, it is desirable that the movable contact be rapidly accelerated toa relatively high speed as it begins its movement toward closedposition, and this high speed should be maintained through the arcingzone and until smooth deceleration is effected at the end of the closingstroke.

It is an object of my invention to provide for a circuit breaker a newand improved dashpot mechanism which effectively controls the speed ofthe movable contact in accordance with the above-described speedrequirements.

It is a further object of my invention to provide, in a dashpotcontrolling a movable contact, a control means which may be operated toadjust the opening speed of the contact in the arcing zone withoutaffecting the contact closing speed in this zone.

It is a further object of my invention to provide for a dashpot anoverflow means which not only compensates for the effect of the pistonrod entering the dashpot cylinder but which also provides a meteringmeans for controlling the speed of movement of the dashpot piston.

It is a still further object of the present invention to incorporatesuch an overflow means into a dashpot mechanism in such a manner thatthe overflow means will facilitate rapid refilling of the dashpotcylinder as the piston rod leaves the cylinder.

Still another object of this invention is to incorporate 2,8M,5l3Patented Aug. 27, 1957 such an overflow means into a contact-controllingdashpot mechanism in such a manner that the overflow means facilitatesinitial acceleration of the moving contact as the closing stroke beginsand in such a manner that the overflow means does not interfere witheffective retardation at the end portion of the contact-opening stroke.

In carrying out my invention in one form, as applied to a circuitbreaker, there is provided a dashpot mechanism comprising a cylinder anda piston reciprocable therein between a closed-contact position and afullyopen contact position. The cylinder is provided with an overflowreservoir compensating for entry of the piston rod into the cylinder,and with an orificed passageway interconnecting the overflow reservoirand the bore of the cylinder and terminating at the bore in a mouthregistering with a metering groove in the bore. This mouth is disposedbetween the closed-contact position and the fully-open contact positionof the piston but adjacent to said fully-open contact position.

The invention will be better understood by considering the followingdescription taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

For a better understanding of my invention reference may be had to theaccompanying drawing in which Fig. 1 is a schematic view of a circuitbreaker organization containing the dashpot mechanism of the presentinvention. Fig. 2 is a top view of the dashpot with portions beingbroken away to illustrate internal details of the dashpot. Fig. 3 is apair of opening and closing curves illustrating the approximateoperating characteristics of the dashpot. Fig. 4 is a schematic view ofthe dashpot in which the dashpot cylinder is disposed in verticalalignment with the abscissa of Fig. 3 so that vertically aligned pointsin these two figures indicate corresponding positions in the stroke ofthe piston. Fig. 5 is an enlarged detailed view of the orificepassageway leading to the overflow reservoir. Fig. 6 is an alternativeform of the orifice construction of Fig. 5.

Referring now to Fig. 1, I have shown my invention as applied to a fluidblast circuit breaker comprising an larc-chute 1 in which there aremounted relatively movable contacts 2 and 3. A conduit 4 communicatingwith a suitable source of gas under pressure (not shown) is provided forsupplying a blast of gas to the arc chute when the contacts areseparated. This blast acts to extinguish the arc which is establishedbetween the contacts when they are separated. The exhaust gases from thearc chute are conducted to atmosphere through a suitable conduit 5.

Opening and closing movement of the contact 2 with respect to contact 3is eifected by means of a reversible fluid motor 10 operatively andinsulatingly connected to contact 2 by a suitable linkage 11.

Since the specific details of the arc chute, the fluid motor, and thelinkage form no part of the present invention, these parts are shown inschematic form only. Preferably, these parts are constructed asdisclosed in Patent 2,436,191, issued to J. W. Timmerman 0n February 17,1948, and assigned to the assignee of the present invention.

The linkage 11 is shown as comprising a rack 12 meshing with a pinion13, the pinion 13 being keyed to a rotatable shaft 14 to which is fixedthe crank arm 15. The movable contact 2 is suitably guided forreciprocation, as by rollers 16, and has pivotally connected thereto aninsulating connecting rod or switch member 17 which is pivotally joinedto the crank arm at 18. It will be apparent from this description thatreciprocation of the rack 12 by the fluid motor 10 will effectreciprocation of the movable contact 2, and correspondingly, the desiredrelative movement between contacts 2 and 3.

In order to provide accurate speed control of the fluid motor and themovable contact 2, I have provided a double-acting dashpot mechanism 2%)which comprises a liquid-filled cylinder 21, in the bore of which there1s mounted a reciprocable piston 22 movable against the resistance ofthe liquid contained in the cylinder. This piston 22 is directly coupledto the fluid motor by means including a piston rod 23 which extends intothe cylinder 21. When the contacts 2, 3 of the circuit breaker areclosed the piston 22 occupies a position at one end of the cylinder 21,as is shown in Fig. l, and when the contacts 2, 3 are fully opened thepiston 22 occupies a position at the opposite end of the cyilnder.

For a more detailed showing of the dashpot mechanism, reference is madeto Fig. 2 wherein the cylinder 21 is shown as comprising a closed-endcylindrical member 24, having tightly fitted therein a cylindricalsleeve 25 having metering slots or grooves 33 and 37 form-ed in itsWall. The cylindrical sleeve 25 is retained in place Within the member24 by means of a plug 26 externally-threaded to engage the cooperatinginternally-threaded outer end of the cylindrical member 24. In order toprevent leakage of the liquid from within the dashpot, there areprovided a pair of packing rings 27 and 28, packing ring 27 beingcompressively retained between plug 26 and a shoulder formed oncylindrical member 24, whereas packing ring 23 fits slidingly butsealing about the piston rod 23.

To aid in controlling the flow of fluid between opposite sides of thepiston 22 as it is reciprocated in the cylinder 21, in a manner to bedescribed in greater detail hereinafter, a series of bypass ductscommunicating with spaced points in the bore of the cylinder areprovided. More particularly, near the left hand end of the cylinder 21,as seen in Fig. 2, there is provided a duct 32 containing a check valve31 permitting fluid flow only to the left. Disposed to the right of duct32 (Fig. 2) is another bypass duct 33 communicating with spaced pointsin the bore of cylinder 21 and containing an adjustable needle valve 34,the setting of which may be varied to vary the fluid flow through bypassduct 33. In parallel fluid flow relationship with duct 33 is anotherbypass 36, which contains a check valve 35 permitting flow through thebypass 36 only to the right, as will be explained in greater detailhereinafter.

By referring to the schematic view of Fig. 4 together with theassociated graphical representation of Fig. 3, wherein verticallyaligned points represent corresponding positions in the stroke of thepiston 22, the operation of the above dashpot will now be described. Asthe contacts of the breaker are parted by the fluid motor 10, the piston22 moves from the closed position at A (Figs. 3 and 4) to anintermediate position at B. During this movement from A to B it ishighly desirable that the movable contact 2 be rapidly accelerated. Toallow for this rapid initial acceleration the dashpot should oflerrelatively little resistance to the piston 22 as it moves from A to B.To this end, liquid flows comparatively freely around the piston 22 boththrough slot 30 as Well as through the then-opened check valve 31 in thebypass duct 32, which extends from A to B. These two passages providerelatively little fluid resistance to fluid flowing around the piston22, hence there is little restriction to piston motion from A to B, andaccordingly the fluid motor 10 may eifect rapid initial acceleration ofthe contact 2, as desired.

As the piston 22 continues in its movement and moves from B to C, thecontact 2 moves through the arcing zone. Through this zone it isdesirable to retard the piston movement and, correspondingly, thecontact movement, so that effective blast action within the are chutecan take place. To this end, I have impeded the flow of fluid about thepiston 22 by providing no bypass groove in the portion of the cylinderwall disposed between B and C. Thus, fluid flow may take place onlythrough the restricted bypass 33 extending from B to C and containingthe adjustable needle valve 34. Check valve 35 prevents fluid flowthrough the bypass duct 36 during piston movement from B to C, whereasthe needle valve 34 permits a restricted amount of flow around thepiston through duct 33. By varying the setting of the needle valve 34,the degree of retardation which takes place as the contact moves throughthe arcing zone can be effectively varied. This adjustment may be set inaccordance with the frequency of the electrical circuit to which thecircuit breaker is to be applied; e. g. more retardation through thearcing zone is desirable in the case of 25 cycle circuits compared tothat suited to the conventional 60 cycle circuit.

As the piston continues in its movement and moves from C to D, thecontact 2 moves out of the arcing zone and, accordingly, it is desirableto resume high speed opening so as to effect rapid isolation of thecontact 2 from contact 3. To this end, there is provided a slot 37 inthe sleeve 25, which slot permits a relatively high rate of flow aboutthe piston 22, thereby permitting rapid movement of the piston from C toD. Because this slot 37 has a portion 38 of substantially uniform crosssection, a controlled and substantially constant speed from C to D isobtained.

To compensate for fluid displaced by the piston rod 23 as it enters thecylinder 24, I have provided an overflow means 40 which comprises aclosed reservoir 41 communicating with the bore of the cylinder througha metering passageway 42 terminating at the cylinder bore in a mouth 43disposed in vertical alignment with the position D. As more clearlyshown in Fig. 5, the passageway 42 contains a metering orifice 44 whichis so proportioned that the fluid flow through the orifice from thecylinder into the reservoir, as the piston moves from A to D, issubstantially equal to the rate at which fluid is being displaced by thepiston rod. This is a desirable characteristic because if the orificewere so large that the fluid flow through the orifice would berelatively unimpeded, insufficient retardation of the piston 22 wouldoccur. Under such conditions, a comparatively large amount of fluidwould flow relatively unimpeded into the reservoir while the flow to'theback side of the piston would be relatively small and a partial vacuumwould be formed on the back side of the piston as it moved from A to D.Thus, it will be seen that the overflow means 40 not only compensatesfor the entry of the piston rod 23, but its metering orifice 44 governsthe fluid flow into the reservoir in a manner effective to contributematerially to the desirable piston-retarding or dashpot effect on piston22, particularly during passage through the arcing zone of the openingstroke.

It is desirable that the speed of the moving contact remain essentiallyunchanged as the piston passes from C through its position at D.However, the presence of the mouth 43 at D presents an obstacle to theattainment of this desired result because, as the forward end of thepiston moves past the mouth 43, the passageway to the overflow means isno longer in parallel flow relationship with the other passage 37 whichmeters fluid around the piston. This parallel relationship existed up tothe time the piston covered the mouth 43, as may be illustrated by thefact that as the piston moved from C to D fluid ahead of the pistonwould flow both through orifice 44 and around the piston through portion38 of slot 37. Now if the mouth 43 were disposed so as to enter the boreat an ungrooved portion of the cylinder, it would follow that as thepiston moved past mouth 43, the passage 42 would be completely shut offfrom communication with the fluid ahead of the piston, as a result ofwhich, the compensating ability of the overflow means would be defeatedat this point so that excessive retardation would occur. T o overcomethis difficulty the mouth 43 is disposed directly in alignment with thegroove 37 so that the passage 42 always remains in communication withthe fluid being displaced through the groove by the piston moving in thecylinder. However, merely aligning the mouth 43 and the groove 37 doesnot restore the parallel fluid flow relationship which existed from C toD, because as the forward surface of the piston moves past the mouth 43,any volume of fluid which flows through the orifice 44 must also flowthrough the slot 37. This condition presents a series fluid flowrelationship of the slot 37 and the orifice 44. To compensate for thistransition from a parallel to a series relationship, I have modified thecross-section of the slot 37 so that its cross sectional area for asubstantial portion 45 of the groove ahead of the mouth 43 is equal tothe sum of the cross sectional area of slot portion 38 and thecross-sectional area of orifice 44. Thus, the slotted portion 45 admitsthe same flow which, from C to D, passed through slotted portion 38 andthe orifice 44. This flow remaining essentially constant, the piston 22moves through its position at D without appreciable change of speed, asis desired. It will be apparent from this description that the reducedgrooved portion 38 controls the flow of fluid to the back side of thepiston until the back surface of the piston moves past grooved portion38. Thus, referring to Fig. 4, the enlargement of groove 37 from portion38 into portion 45 may begin at any point between the mouth 43 and apoint spaced from the mouth to the left by a distance equal to theeffective thickness of the piston.

As the piston nears the end of the cylinder at B, it is desirable tosmoothly decelerate the piston and the associated contact. To this end,the slot 37 is tapered toward the end of the cylinder so as to admitaconstantly diminishing flow of fluid past piston 22.

The above described opening operation is illustrated in Fig. 3 by thecurve X from which it will be observed that from A to B the piston israpidly accelerated, but

as the piston enters the arcing zone extending from B to C the piston isretarded, as desired, as indicated by the relatively steep slope ofcurve X between B and C. When the piston leaves this arcing zone, rapidopening speed is resumed and continued through D until smoothdeceleration occurs at the end of the opening stroke at E.

In contrast to this variable speed opening operation, contact closingshould be effected at high speed without retardation in the arcing zone.Thus, it is desirable that the piston be rapidly accelerated to arelatively high speed as it begins its movement toward closed position,and this high speed should be maintained through the arcing zone anduntil smooth deceleration is effected at the end of the closing stroke.

To produce this desired rapid initial acceleration as closing operationis initiated and the piston moves from E to D, fluid ahead of the piston22 is permitted to flow in any of three different paths, i. e., throughslot 37, through the check valve 46 in the piston 22, and into theoverflow means 40. Thus it will be seen that disposing the mouth of theoverflow at a point spaced from the pistons fully open contact positionat E provides an additional fluid flow path which desirably permitsfaster acceleration as soon as a closing operation is initiated.

As the closing operation continues and the piston moves from D to C,fluid readily transfers to the back of the piston through check valve 46and slotted portion 38, thus permitting closing to continue at highspeed, as desired. As closing continues and the piston moves from C toB, i. e., the grooveless portion of the cylinder, fluid flowscomparatively freely through the then open check valve 35 in duct 36thus effectively shunting the restricted needle valve 34. This shuntingof the needle valve permits the piston to sustain its velocity as thecontact 2 moves through the arcing zone to close the circuit, as isdesired. Preferably, the restricted passage through valve 35 is ofsubstantially the ,same cross-section as slotted portion 38, so that nosubstantial change of speed occurs as the piston moves through thearcing zone toward closed position.

The desired smooth retardation at the end of the closing stroke iseflected by the taper formed in groove 30. The duct 32 which was used topermit initial opening acceleration is effectively prevented frominterfering with retardation at the end of this closing stroke by meansof the now closed check valve 31. This check valve 31 introducesretardation between A and B during closing which was not present duringopening. I

The above-described closing operation is illustrated in Fig. 3 by thecurve Y which shows that the piston is rapidly accelerated to arelatively high speed as closing operation begins, and this high speedis maintained throughout most of the stroke, as indicated by thesubstantially constant slope of most of curve Y. Finally, smooth deceleration occurs at the end of the closing stroke.

It should be noted that as the piston 22 moves past the mouth 43 andtoward its closed position at A, fluid is flowing from the reservoir tothe cylinder through the orifice 44 to maintain the cylinder 24 inliquid-filled condition and thereby to compensate for the effect of thepiston rod 23 leaving the cylinder.

It will become apparent as the description proceeds that the location ofthe mouth 43 of the overflow passageway at a point in the cylinder boredisposed intermediate the closed and fully open contact positions butadjacent to and spaced from the fully open contact position at E is animportant feature of the dashpot mechanism of this invention. This maybe illustrated by a description of the characteristics of the dashpotunder trip-free closing operation of the breaker contact 2. For example,assume that when contact 2 is moved from open toward closed position, afault is present on the line and, as a result, it is necessary for thepiston 22 to rapidly reverse its direction of movement as it nears theend of its closing stroke. When this rapid reversal occurs, if thecylinder is not filled with liquid on the forward side of the reversedpiston, the reversely moving piston will be oifered little resistanceuntil the cylinder space ahead of it becomes refilled with liquid. Undersuch conditions the reversely moving piston would accelerate rapidlyuntil the instant it had diminished the cylinder space ahead of itsufficiently to produce a fluid-filled condition. At such an instant,the piston would be abruptly decelerated, thereby producing highlyundesirable shock conditions in the breaker mechanism. To avoid theseundesirable shock conditions, rapid refilling of the dashpot cylinderbehind the piston should be effected as the piston moves toward closedposition. I have achieved this desired result, in part, by locating themouth 43 of the overflow passageway near the fully open contact positionof the piston. Since this month 43 is located on the low pressure sideof the piston throughout the greater part of the closing stroke, fluidfrom overflow reservoir may pass directly into the space on the lowpressure side behind the piston during the greater portion of thisclosing stroke. Thus, favorable conditions for rapid refilling areprovided as a result of the location of mouth 43. Still another factorwhich contributes to rapid refilling during the closing stroke is thefact that the reservoir 41 is a closed chamber so that air entrappedtherein provides the system with what amounts to an air cushion. Thus,since the air entrapped above the fluid is pressurized during theopening stroke, it expands during closing to provide an appreciablepositive pressure forcing the fluid from the overflow back into thecylinder, thereby facilitating rapid refilling of the cylinder duringclosing operation.

Another important consideration in locating the mouth 43 of thepassageway 42 is that the overflow means should not interfere withdeceleration of the piston at the end of the contact opening stroke. Tothis end, the mouth 43 is located at a point spaced from the pistonsfully open contact position at E, so that the tapered portion of groove37 can provide sufiicient deceleration of the piston at the 7 endportion of the opening stroke. Another advantage of this location of themouth 43 is that, with the mouth so located, the overflow means actuallyaids in effecting the desired rapid initial acceleration of the pistonas the closing stroke is begun. This is so because the passageway 42provides an additional path through which fluid ahead of the piston mayflow as the closing stroke is initiated.

Thus, it will be seen that the overflow means of the present inventionis so constructed and so located that it effectively contributes to thedesired rapid refilling of the cylinder and to allowing for rapidacceleration of the piston as the closing stroke is initiated.Additionally, the overflow means accomplishes these results withoutinterfering with the desired retardation at the end of opening stroke.

To further insure that the dashpot cylinder will be filled as the pistonis moved toward closed position, I have provided an alternative form oforifice which may be used instead of the orifice 44 of Figure 5. Thisalternative orifice construction is disclosed in Fig. 6 wherein anorifice 50 is shown as being formed in a check valve 51 which islightlyspring biased toward closed position. Orifice 50 will function inthe same metering manner as orifice 44 so long as fluid flow is into theoverflow reservoir, but when fluid flow is in the opposite direction,the check valve 51 is displaced from its seat thereby permitting a largeflow from the reservoir into the cylinder, thus facilitating the desiredrapid refilling of the cylinder as the piston moves towardcontact-closed position.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects and I, therefore, intend in theappended claims to cover all such changes and modifications as fallWithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a circuit breaker having a contact movable between a closedposition and a fully open position and a switch member for moving saidcontact, a dashpot mechanism for controlling the speed of movement ofsaid contact comprising a liquid-filled cylinder having a reciprocablepiston therein, a piston rod coupling said switch member to said pistonfor movement of said piston between spaced apart closed and fully openpositions in said cylinder as said contact is moved between its closedand fully open positions respectively, a piston-rod compensatingoverflow reservoir, an orificed metering passageway connecting saidreservoir with :a point in said cylinder intermediate said closed andfully open piston positions and adjacent but spaced from said fully openpiston position.

2. In a circuit breaker having a contact movable between a closedposition and a fully open position, a dashpot mechanism for controllingthe speed of movement of said contact, said dashpot mechanism comprisinga cylinder having a bore and a reciprocable piston disposed therein,means including a piston rod coupling said contact to said piston in amanner whereby said piston moves between spaced-apart closed and fullyopen positions in said bore when said contact is moved between itsclosed and fully open positions respectively, said dashpot mechanismincluding an overflow reservoir which compensates for the effect of saidpiston rod entering and leaving said cylinder, an orificed meteringpassageway interconnecting said reservoir and said bore and enteringsaid bore through a mouth located intermediate said closed and fullyopen piston positions but adjacent to and spaced from said fully openpiston position.

3. In a circuit breaker having a contact movable between a closedposition and a fully open position, a dashpot mechanism for controllingthe speed of movement of said contact comprising a cylinder having abore, a

reciprocable piston movable between spaced-apart closed .said. borethrough a mouth located intermediate said closed and fully open pistonpositions but adjacent to and spaced from said fully open pistonposition, said overflow reservoir being completely enclosed except forthe opening provided for entry of said metering passageway.

4. In a circuit breaker having a contact movable between a closedposition and a fully open position, a dashpot mechanism for controllingthe speed of movement of said contact, said dashpot mechanism comprisinga cylinder having a bore containing a reciprocable piston, meansincluding a piston rod coupling said contact to said piston in a mannerwhereby the piston moves between spacedapart closed and fully openpositions in said bore when said contact is moved between closed andfully open positions respectively, said dashpot mechanism including anoverflow reservoir which compensates for the effect of said piston rodentering and leaving said cylinder, said overflow reservoircommunicating with the bore of said cylinder through an orificedmetering passageway which enters said bore through a mouth locatedintermediate said closed and fully open piston position but adjacent toand spaced from said fully open piston position, said cylinder having agenerally axially extending metering groove in its bore, said meteringgroove being disposed in registry with said mouth and extending onopposite sides of said mouth.

5. The combination of claim 4 in which said groove is enlarged at anedge of said mouth so as to permit said piston to move past said mouthwithout appreciable change of speed.

6. In a circuit breaker having a contact movable between a closedposition and a fully open position, a dashpot mechanism for governingthe speed of movement of said contact, said dashpot mechanism comprisinga cylinder having a bore, a reciprocable piston movable between spacedapart closed and fully open positions in said bore when said contact ismoved between closed and fully open positions respectively, said pistonbeing actuated through a piston rod coupled to said contact, saiddashpot mechanism including an overflow reservoir which compensates forthe effect of said piston rod entering and leaving said cylinder, ametering passageway interconnecting said reservoir and said bore andentering said bore through a mouth located intermediate said closed andfully open positions but adjacent to and spaced from said fully openpiston position, a check valve disposed in said metering passageway andhaving an orifice formed therein, said check valve permitting greaterflow from said reservoir than into said'reservoir.

7. A dashpot mechanism comprising a cylinder containing a fluid, apiston movable within the bore of said cylinder, a piston rod extendinginto said cylinder and arranged to produce reciprocation of said pistonagainst the resistance of said fluid, an overflow reservoir compensatingfor the displacement of fluid by said piston rod, a passagewayinterconnecting said reservoir and said bore and terminating at saidbore in a mouth, the bore of said cylinder having a metering grooveregistering with said mouth and extending axially of said bore onopposite sides of said mouth, said metering groove having a firstportion extending for a substantial axial distance on one side of saidmouth and a second portion disposed essentially on the other side onlyof said mouth, said first portion of said groove having across-sectional area substantially greater than the cross-sectional areaof said second portion in the region where said two groove portionsmeet.

8. The dashpot mechanism of claim 7 in which said passageway contains ametering orifice of a predetermined cross-sectional area, said firstportion of said metering groove having a cross-sectional areasubstantially equal to the sum of the cross-sectional area of saidorifice plus the cross sectional area of said second portion of saidmetering groove.

9. A dashpot mechanism comprising a cylinder containing a fluid, apiston movable within the bore of said cylinder, a piston rod extendinginto said cylinder through an end wall thereof and arranged to producereciprocation of said piston against the resistance of said fluid, anoverflow reservoir compensating for the displacement of fluid by saidpiston rod, a passageway interconnecting said reservoir and said boreand terminating at said bore in a mouth, the bore of said cylinderhaving a metering groove registering with said mouth and extendingaxially of said bore on opposite sides of said month, said meteringgroove having a first portion extending for a substantial axial distanceon one side of said mouth and a second portion disposed essentially onthe other side only of said mouth, said first portion of said groovehaving a cross-sectional area substantially greater than thecross-sectional area of said second portion in the region where said twogroove portions meet, the enlarged portion of the metering groove beingdisposed on that side of said month which is axially opposed to thecylinder wall through which the piston rod enters said cylinder.

10. A dashpot mechanism comprising a cylinder containing a fluid, apiston movable within the bore of said cylinder, a piston rod extendinginto said cylinder and arranged to produce reciprocation of said pistonagainst the resistance of said fluid, an overflow reservoir compensatingfor the displacement of fluid by said piston rod, a passagewayinterconnecting said reservoir and said bore and terminating at saidbore in a mouth, the bore of said cylinder having a metering grooveregistering with said mouth and extending axially of said bore onopposite sides of said mouth, said metering groove having a firstportion of substantially uniform cross-section extending for asubstantial axial distance on one side of said mouth and a secondportion of substantially uniform crosssection disposed essentially onthe other side only of said mouth, said first portion of said groovehaving a crosssectional area substantially greater than thecross-sectional area of said second portion in the region where said twogroove portions meet.

11. A dashpot mechanism comprising a cylinder containing a fluid, apiston movable within the bore of said cylinder, a piston rod extendinginto said cylinder and arranged to produce reciprocation of said pistonagainst the resistance of said fluid, an overflow reservoir compensatingfor the displacement of fluid by said piston rod, a passagewayinterconnecting said reservoir and said bore and terminating at saidbore in a mouth, the bore of said cylinder containing a metering grooveregistering with said mouth and extending axially along said bore onopposite sides of said mouth, said groove having a first portion locatedon one side only of said mouth and extending for a substantial axialdistance from said one side of said mouth and a second portion extendingon the other side of said mouth from a point axially spaced from themouth by a distance not exceeding the effective thickness of saidpiston, said first portion having a substantially larger cross-sectionalarea than said second portion in the region where said two portionsmeet.

12. In a circuit breaker having a contact movable between a closedposition and a fully open position and through an arcing zone disposedbetween said two positions, a dashpot mechanism for governing the speedof said contact, said dashpot mechanism comprising a cylinder enclosinga reciprocable piston coupled to said contact so as to occupy a firstposition at one end of the bore of said cylinder when said contact is inclosed position and a second position at the opposite end of said borewhen said contact is in fully-open position, an intermediate portion ofsaid bore corresponding to said arcing zone, and control means foradjusting the speed of the piston as it moves through said arcing zonefrom said first portion to said second position, said control meanscomprising a pair of bypass ducts communicating with said bore at pointscorresponding to the limits of said arcing zone, said ducts being inparallel flow relationship and one of said ducts containing a checkvalve.

13. In a circuit breaker having a contact movable between a closedposition and a fully-open position and through an arcing zone disposedbetween said two positions, a dashpot mechanism for governing the speedof said contact, said dashpot mechanism comprising a cylinder enclosinga reciprocable piston coupled to said contact so as to occupy a firstposition at one end of the bore of said cylinder when said contact is inclosed position and a second position at the opposite end of said borewhen said contact is in fully-open position, an intermediate portion ofsaid bore corresponding to said arcing zone, and control means foradjusting the speed of the piston as it moves through said arcing zonefrom said first position to said second position, said control meanscomprising a bypass duct and a check valve arranged in said duct in sucha manner that adjustment of said control means has no substantial eflecton the speed of the piston as it moves through said arcing zone fromsaid second position to said first position.

14. In a circuit breaker having a contact movable between a closedposition and a fully open position and through an arcing zone disposedbetween said two positions, a dashpot mechanism for governing the speedof said contact, said dashpot mechanism comprising a cylinder, areciprocable piston movable within the bore of said cylinder and coupledto said contact so as to occupy a first position at one end of said borewhen said contact is in closed position and a second position at theopposite end of said bore when said contact is in fully open position,an intermediate portion of said bore corresponding to said arcing zone,and control means for adjusting the speed of the piston as it movesthrough said arcing zone from said first position to said secondposition, said control means comprising a pair of bypass ducts arrangedin parallel flow relationship and communicating with said bore at pointscorresponding to the limits of said arcing zone, a check valve disposedin one of said ducts and arranged to block flow through said one ductduring movement of said piston through said arcing zone in a directionfrom said first to said second position.

15. The arrangement of claim 14 in combination with an adjustable valvewhich is disposed in the second of said ducts and is adjustable tocontrol the flow of fluid through said second duct.

16. In a circuit breaker having a contact movable between a closedposition and a fully open position, a dashpot mechanism for controllingthe speed of movement of said contact, said dashpot mechanism comprisinga cylinder having a bore and a reciprocable piston disposed therein,means including a piston rod coupling said contact to said piston in amanner whereby said piston moves between spaced apart closed and fullyopen positions in said bore when said contact is moved between itsclosed and fully-open positions respectively, said dashpot mechanismincluding an overflow reservoir which compensates for the efiect of saidpiston rod entering and leaving said cylinder, an orificed meter- 11 7 7ing passageway interconnecting said reservoir and sai 1,724,571 bore andentering said bore through a mouth located ad- 2,040,262 jacent to saidfully-open piston position. 2,298,208

References Cited in the file of this patent 5 UNITED STATES PATENTS1,689,841 Powell Oct, 30, 1928 12 Fiddyment Aug. 13, 1929' Kruckenberget a1 -1 May 12, 1936 Gilbert et a1. Oct. 6, 1942 FOREIGN PATENTS FranceJuly 6, 1926

